Preheat oven to 350°F. Line a 8-inch square baking dish with parchment paper, allowing the sides to hang off. Set aside.

To make the shortbread crust, in the bowl of an electric mixer, cream together the butter and granulated sugar, for about 3 minutes, until creamy. Stir in the vanilla extract. Use a spatula to scrape down the bottom and sides of the bowl, and stir once more. Slowly add the flour and salt and mix until the dough comes together and pulls away from the sides. Dump the dough into the prepared pan and press out evenly with lightly floured hands. Bake for about 20 minutes or until the edges are golden brown. Remove from the oven and let cool.

To make the caramel, fill a pot with water, halfway up, and bring to a boil. Reduce the heat and place a heat-proof bowl over the simmering water, making sure the bottom of the bowl doesn't touch the water. Add the condensed milk, peanut butter, and brown sugar to the bowl. Stir until completely smooth and cook for about 3 to 6 minutes until the mixture has slightly thickened and come together. Remove the bowl from over the boiling water and fold in the chopped peanuts. Pour the caramel over the cooled shortbread crust. Evenly smooth it out, making sure to cover the crust completely. Place in the fridge and allow to chill for at least 30 minutes.

Bring the water to a boil once more and place a heat proof bowl over, making sure the bottom of the bowl doesn't touch the water. Melt the chocolate in the double boiler, stirring frequently until completely smooth. Remove from heat and pour over the chilled caramel. Spread out evenly and top with the chopped pretzels. Place back in the fridge for another 30 minutes before slicing. Remove the bars from the pan, using the excess parchment paper. Cut into even pieces and store any leftovers in the fridge. Will keep up to a week, or a few weeks in the freezer. Enjoy!